Antenna arrays having multiple elements have been used extensively in direction-finding in which the direction of the major lobe of the array, as well as the side lobe configuration, is determined by a number of active and passive elements in the array. When these arrays are deployed, for instance, on aircraft, the array assembly is first manufactured and then located in a housing commensurate with the application. For instance, in aircraft configurations, the antenna array is housed in pods or in Fiberglas housings, which are then deployed on the aircraft.
The problem in manufacturing such multi-element arrays is the testing of the arrays prior to encapsulation or mounting on the vehicle, vessel or aircraft. The major problem in the manufacture of such arrays is improper termination of the passive elements of the array, usually involving poor termination soldering.
As to the active elements of the array, their proper operation can be tested by cabling the active elements to a back plane where the standing wave ratio of the active elements can be ascertained in a conventional manner. Moreover, proper operation of such an array can be ascertained in the far field by mounting the antenna array at the center of a rather large antenna range and detecting the radiation pattern. This is effective to ascertain if the radiation pattern matches the desired radiation pattern, but in no way indicates what element or elements are faulty in the array. Moreover, transporting an antenna to a facility is uneconomical at best and impractical in most instances because, for instance, if antenna arrays are to be mass-produced at 10 per day, it would be impractical to transport the antenna arrays to an antenna range that may be some miles from the manufacturing facility.
The major defects of such arrays are in the passive elements, which are terminated in most cases by a 50-ohm resistor at the input to the passive element. In a large number of cases, the passive elements could be Vivaldi notch antennas, dipoles, monopoles or V antennas; or in fact any convenient antenna configuration. In general, microwave antennas are terminated with chip-type surface mount resistors that are soldered onto the antenna adjacent the feedpoint.
Oftentimes it is not possible to ascertain whether the termination is effective by visual inspection means. Thus some type of testing must be employed to ascertain if the antenna that has been manufactured meets the specifications. For instance, if one or more of the passive elements of the antenna array are improperly terminated or are unterminated, then the resulting antenna pattern is seriously distorted, making it unusable in direction-finding applications.
In the past, such antennas were checked in a quality control environment utilizing terminated dummy antennas, which are very complex to build. Cables were run to the dummy antennas and terminated with 50 ohms at a back plane, involving excessive cost and potential damage to the antenna when the cables were moved.
In later years the complicated cabling process was discarded in favor of terminations placed at the antenna feedpoint after testing. Instead of the cables coming back and being terminated with 50 ohms, the passive antenna element was terminated right at the feedpoint.
Thus, rather than building antennas that had both active and passive elements, with all elements having cables running back through cables to 50-ohm terminations, presently these antennas are fabricated with the 50-ohm termination at the particular passive antenna element.
This method of fabricating antenna arrays is not easily checked after manufacture other than by transporting the finished antenna array to the antenna range, of which there are very few in existence.
In summary, because there are passive elements in the array in which there are no cables involved, there is a problem in providing an efficient testing system for the directional antennas, especially in high-volume production applications.
The task is to obtain the antenna arrays coming off the production line and to rapidly test them before they go onto the next step, which involves embedding the array into a structure to be mounted for a particular application. The task is to make sure that the antenna array is working properly before other production processes take place, such as, for instance, delivery for integration into whatever platform they are to be used in. If one were to be able to test the array and find out if there is a problem, the problem could be repaired prior to integration. However, if one waited until after integration, if the antenna array proved defective it could not be readily repaired.
These antenna arrays in general for direction-finding purposes include tapered blades, standard dipoles or broadband monopoles or dipoles, and it is an urgent matter to be able to test them bare. Once they get wrapped in Fiberglas for anti-ice protection and the like, they cannot be readily fixed.
In summary, prior antenna array testing techniques were at best cumbersome and highly expensive; and more importantly could not identify what antenna element was defective, meaning unterminated or improperly terminated. All that could be done, even in the antenna range case, would be to ascertain that the antenna pattern was not that which was specified.